Most geological reservoirs are formed by porous rock formations which are saturated with fluids such as oil, gas, and/or water. The ease at which these fluids can be produced from such underground reservoirs depends, in part, upon the permeability of the formation containing the fluid. The permeability of the formation near the well bore is particularly important to the productivity of a well because fluid from throughout the reservoir must flow through a relatively small surface area, or "skin", at the face of the well bore. Since many well bores are also lined with a cemented casing pipe, flow from the reservoir may be further restricted at the face of the well bore by the effectiveness of the perforations through the casing and cement. It is therefore important to maintain the permeability of the formation near the well bore and, more particularly, in and around the perforations in any casing that may line the well bore.
A variety of factors may cause damage to the "skin" of the formation immediately surrounding a well bore. For example, pressure and/or temperature changes during production cycles of a well can significantly increase the deposition of various materials in and around the well bore. Paraffin waxes and other heavy hydrocarbon residues are common precipitates in oil and gas wells while assorted mineral scales, including gypsum and calcium carbonate, are often deposited in oil and water wells. Permeability near the well bore may also be affected by a variety of other factors including bacterial proliferation, casing corrosion, formation deterioration, and emulsive mixing of the oil, gas, and/or water.
Many different chemical agents, both preventative and remedial, have been developed in an attempt to treat the various causes of reduced permeability near the well bore. Although each of these agents can be shown to be quite effective at treating blockages in the laboratory, it has been found to be difficult, in practice, to repeat such successes in the field. The present invention addresses these practical difficulties that may be caused at least in part, by insufficient contact of the treating fluids with the formation skin. The present invention provides an advantageous method and apparatus for addressing these and other problems associated with conventional well treatment technologies.
U.S. Pat. No. 2,055,515 to Yarborough, discloses a conventional cleaning apparatus for perforated pipe and the like. FIG. 4 of Yarborough shows a cleaner which is adapted to slosh production fluids back and forth through perforations in a restricted area of a strainer pipe. In operation, the tool is lowered into the well until packing members are arranged on either side of a desired interval. A plunger rod is then reciprocated to alternately apply suction and pressure to the confined interval, thereby sloshes the well fluid back and forth through the perforations.
The packing members disclosed in Yarborough are problematic because they often fail to seal properly and can jam the tool inside the well bore. Furthermore, since devices like that disclosed in Yarborough merely slosh production fluids back and forth through the casing (the so-called "washing effect" described at page 4, first column, line 27 of Yarborough), they do not allow fresh chemical treatment fluids to be used to clean the perforations. Moreover, the amount of fluid displaced by the device which is disclosed in the Yarborough patent is limited by the length of the tool stroke.
U.S. Pat. No. 3,760,878 to Peevey discloses a tool which is connected to a lower end of a string of tubing for washing perforations in a casing. The tool has three cup type packers which, in operation, are placed so that the perforations to be washed are below the lower two packers. Cleaning fluid is circulated down the annulus through an upper port of the housing and out a lower port between the lower two packers where it flows into the perforations. The cleaning fluid returns through perforations which are below the lower packer and then flows up into the tubing into the interior of the tool. As with Yarborough, the Peevey tool is also problematic because it uses packers.
The present invention relates to a method of treating a well using a tool string including a pump. The method may include the steps of supplying a predetermined amount of treatment fluid to the well, pumping the treatment fluid from the well bore into the tool string, and releasing the treatment fluid from the tool string into the well.
The present invention also relates to a method of treating a well using a tool string including a pump and a dump valve. The method may include the steps of filling the tool with a treatment fluid, opening the dump valve to release the treatment fluid from the tool string back into the well bore, and reciprocating the tool string in order to pump the treatment fluid from the well bore into the tool string.
The present invention also relates to an apparatus for storing fluid from a well bore. The apparatus may include a tubing string, a reservoir for storing treatment fluid within the tubing string, openings in the tubing string at a lower portion of the reservoir, and means for selectively opening and closing said openings in the tubing string.
In a further aspect of the present invention, the apparatus may include a dump valve arranged above a formation interval which is to be treated. The dump valve may be opened in order to allow treatment fluid to flow out of the tubing and create turbulent mixing currents as the treatment fluid flows down the well bore and covers the perforations. A still further aspect of the present invention includes adding additional treatment fluid to periodically revitalize the fluid and create additional hydrostatic head for enhanced turbulence when a predetermined amount of treatment fluid flows into the formation.